Process For Enhanced 3D Integration and Structures Generated Using the Same

ABSTRACT

An enhanced 3D integration structure comprises a logic microprocessor chip bonded to a collection of vertically stacked memory slices and an optional set of outer vertical slices comprising optoelectronic devices. Such a device enables both high memory content in close proximity to the logic circuits and a high bandwidth for logic to memory communication. Additionally, the provision of optoelectronic devices in the outer slices of the vertical slice stack enables high bandwidth direct communication between logic processor chips on adjacent enhanced 3D modules mounted next to each other or on adjacent packaging substrates. A method to fabricate such structures comprises using a template assembly which enables wafer format processing of vertical slice stacks.

STATEMENT PURSUANT TO 37 C.F.R. §1.77 (B) (3) REGARDING FEDERALLYSPONSORED RESEARCH OR DEVELOPMENT

This invention was made under a federally sponsored research anddevelopment agreement, H98230-08-C-1468, “CYCLOPS II ARCHITECTURE andENGINEERING STUDY.”

FIELD OF THE INVENTION

The field of the invention comprises integrated electronic 3D systemdevices and a process for building integrated 3D system devices thatenables a higher level of system integration than possible with current3D integration processes and structures, but does not employ throughsilicon vias.

BACKGROUND OF THE INVENTION AND RELATED ART

Various processes and structures described in the related art addresshigh level system integration such as Hoffman, et al., U.S. Pat. No.6,033,931, one of a class of so-called “cube patents.” Hoffman, et al.discloses a three-dimensional microchip circuit assembly process thatemploys a three-layer dry film sandwich to prepare a stacked circuitcube. Bertin, et al. U.S. Pat. No. 5,563,086 discloses an integratedmemory cube structure and method of fabrication in which stackedsemiconductor memory chips are integrated by a controlling logic chipsuch that a more powerful memory architecture is defined with thefunctional appearance of a single higher level memory chip. Carson, etal., U.S. Pat. No. 5,347,428 describes a computer module in which astack of glued together IC memory chips is structurally integrated withan IC microprocessor chip. Go, et al. U.S. Pat. No. 5,104,820 disclosesa method of fabricating electronic circuitry units containing stacked IClayers having lead rerouting. Carson, et al., U.S. Pat. No. 4,646,128discloses high-density electronic processing packages and structures andmethods for manufacturing them.

The so-called “cube” structures described in these references is aresult of a procedure also known in the art as chip stacking, but thishas several drawbacks that include inter alia; edge connectionarchitecture which leads to signal delay, lower input/output (I/O)density, difficulty in powering the system through edge connections, anddifficulty in cooling the system for high power use.

Scaling of complementary metal-oxide-semiconductors (CMOS) transistordevices to smaller and smaller dimensions to enable larger circuitdensity is running into challenges in that the performance of such ultrasmall devices is not scaling favorably due to short channel effects inthe device behavior, the difficulty in scaling channel strain inducedmobility enhancements and the like. Additionally, with the increasedlogic circuit density, the demands for memory accessible by logiccircuits with minimal delay and memory bandwidth to access a largesegment of the memory at a given time are becoming paramount toachieving peak performance. This in turn drives two requirements. First,additional memory needs to be located close to the logic circuitry withfast access time and second, high bandwidth interconnects are requiredfor the logic circuits to send and retrieve information from thesememory cells on the chip thus driving a huge increase in interconnectdensity and speed.

In this regard, 3D integration (3DI) which represents a process fordevice integration at a system level is emerging as an option to bringheterogeneous devices together in close proximity so that they functionas a homogeneous device. 3DI differs from the traditional 2D planarback-end-of-line (BEOL) integration in that 3DI adds an additionaldimension, (Z) integration, which allows more devices from differentsources, functionalities, and types to be integrated in a closeproximity to form a single assembly which can function as an integratedsystem.

The 3DI approach allows more device content (memory for example) andfast access time to the various devices (shorter signal travel distanceenabled through connections in the Z-direction) than the traditional 2Dplanar structure restricted to X-Y wiring only. This is very beneficialfor system level performance since the accessible amount of memorywithin one clock-cycle distance can be greatly enhanced by shorteningthe physical distance between the processor and memory elements of thesystem. A clock-cycle distance is the distance that the signal can coverwithin one device clock-cycle. For today's devices running at overseveral GHz speed this distance is reduced to only several millimeters.In a 2D configuration more and more device contents have to be placedoutside this distance. Thus more clock-cycles are needed to access themduring complex operations requiring a large amount of memory to beretrieved, processed, and stored back. This in turn translates intoslower data processing speed at the system level although the individualelements of the system—processor and memory—are capable of higher speedof operation.

3D integration places the additional contents such as memory cells inthe third dimension (by Z-stacking), and therefore increases the amountof accessible device functionality within the critical singleclock-cycle zone. In addition to more memory content within theclock-cycle zone, 3DI also allows additional and disparate componentssuch as SiGe, III-V devices, optoelectronics, MEMS and the like to beintegrated as part of the system on a single assembly level. As thesecomponents are typically fabricated on different substrates usingprocesses which may be incompatible with currently practiced siliconCMOS processes, they cannot be embedded into a silicon chip using 2Dprocess methodologies. Thus such components tend to be integrated withCMOS using chip carriers or circuit boards as a means to interconnectthem which can limit the ability to fully utilize the capability of thecomponents.

Of the process format, 3DI can be further separated into wire bondedchip stacks and through silicon via (TSV) based chip stacks. The wirebonded 3DI mainly focuses on lower density and count input/output (I/O).Typically dozens to hundreds of I/O's, and are used for systems wherehigh contents and lower power within a given footprint are the keyconsiderations for the consumer markets. These typically use wire bondconnections at the periphery of the stacked wafers to achieve I/Oconnections. The TSV 3DI on the other hand tends to focus on highperformance systems where I/O count is over several thousands and highspeed (>2 GHz) processors are used where the system clock-distancebecomes a key requirement. In this high performance application space,through Si via connections become a dominant factor by enabling shortervertical connections to reduce distance between the devices

For most chip-level 3DI, chip stacking is used along with the provisionof device I/O fanned out to edge leads. The edge leads are thenconnected with wire bonds to edge pads on a logic chip of a larger sizeplaced at the bottom of the chip stack. Due to such a connection scheme,chip-level connection typically enables more content than 2D but theaccess time between devices is limited by inductive and capacitivedelays associated with the bonded wire connections and going to theedges of the chips. Also it is difficult to conveniently deliver powerto the various chips in the stacked assembly.

3DI with through-Si-via connection allows the integration at wafer leveland offers a higher I/O density and a Z-connection with reducedparasitics compared to wire bond connections. Through-Si-via processesfor 3DI can also be further separated into via-first and via lastapproaches. Via-first as the name implies comprises embedding thethrough vias in the parent wafer(s) before devices are fabricated. Thisnormally allows a higher wiring content since the I/O's do not gothrough the top device structure directly thus allowing more area forwiring. The level to level z-connections are typically done betweencapture pads on the through vias using metal compression bonds (usingmetals such as Cu—Cu, no solder, no adhesive), micro-C4 joining (solder,no adhesive), or transfer joining (T&J, metal compression bondsupplemented by adhesive joining for strength referred to as hybridbonding). Via-first connections typically enable an I/O density withpitch as small as about 25 to about 50 microns (um). The assemblymethods described above can also be used for individual chips, and arenot restricted to just wafer level 3DI schemes.

For 3DI with via-last approach, the wiring density is typically reducedrelative to the via first approach due to the use of some of the wiringchannels by the thru-vias which need to thread through the entire devicestack to connect devices. However, since the thru-vias can be definedlithographically and filled, they are not limited by the 3D layerjoining tolerances as in the case of the via first approach, via-lastnormally can have a higher via-density (under about 5 um pitch) thanvia-first approach (about 25 to about 50 um pitch).

In all 3DI integration schemes mentioned above, the cooling of thesystem is typically a difficult issue to resolve. The tighter stackingof devices generates more heat per unit volume but with reduced heatdissipation. Provision of micro-channels for cooling on the bulk siliconsubstrate of the assembly in the final 3DI stack can provide enhancedcooling but cannot completely achieve an effective cooling of upperlayers when many device layers are stacked in the 3D system. Thus forboth chip stacking and through-Si connection approaches, the heatingpower density increases as the number of 3DI devices increase. Thislimits the number of 3DI devices stackable into a system as the heatdissipation becomes a road block for further 3D content increase.

Another issue associated with 3DI is the thru-Si connectionelectro-static discharge (ESD) protection requirements. In any devicedesign, an ESD protection circuitry is provided and linked to an I/Onet. This protects sensitive devices from manufacturing process inducedESD. Since each wafer in a 3DI stack needs ESD protection, the final 3DIcircuits will have to have a total ESD circuit allocation as large asthe sum of all the devices in the 3DI structure. This can be a largeload as the number of devices increases and requires a large driver toaccess the 3DI circuits which could significantly slow them down.

In general, the current thru-Si 3D wafer stacking processes andresultant devices present many processing related issues, e.g., thin Siconstruction (<100 um) requires stacking wafers one at a time to allowthru-Si vias; it is difficult to make the via less than 5 um in size and10 um in pitch in devices employing Cu; thru-Si vias can be made from Wbut W has a higher resistivity than Cu; thru-Si vias pass through thebonding interface making bonding defects difficult to control; waferstacks are limited due to bonding thermal cycles; the process is complexand introduces via yield and wafer yield issues; manufacturing involveslong process cycles; wafer level distortions are introduced.Accommodation of thru-Si vias requires significant changes in the layout of processor and memory chips in addition to leading to loss ofuseable silicon area available for device circuits. The chip cubeapproaches known in the current art which avoid thru-Si via relatedconcerns, however are limited in their ability to provide a highbandwidth for data communication in and out of the structure and havehigh parasitics as they depend on edge leads or wire bonds formed afterassembly.

SUMMARY OF THE INVENTION

The present invention provides structures, articles of manufacture andprocesses that address these difficulties and needs, to not only provideadvantages over the related art, but also to substantially obviate oneor more of the foregoing and other limitations and disadvantages of therelated art by providing processes for enhanced 3D integration andstructures generated by these processes.

Not only do the written description, claims, abstract of the disclosure,and the drawings that follow set forth various features, objectives, andadvantages of the invention and how they may be realized and obtained,but these features, objectives, and advantages will also become apparentby practicing the invention.

To achieve these and other advantages, and in accordance with thepurpose of the invention as embodied and broadly described herein, theinvention comprises inter alia, an integration technique that enablesthe increase of the accessible system memory within one processorclock-cycle by 10 fold or more as compared to a 2D system. Such anincrease in memory content is in excess of the few fold increasepossible with conventional 3DI stacking of memory wafers/chips onprocessor base wafer/chip.

The object of the present invention is to further tackle and solve theabove mentioned limitations and disadvantages of the TSV based 3DIapproaches, and comprises an enhanced TSV-free 3DI approach denoted as“4D Integration” (4DI for short).

Many of the enhancements are described in the co-pending applicationYOR920090121US1 by some of the present authors attached herewith forreference. The present application describes a simple method to producethe 4DI assembly using wafer type substrate format processing.Additionally, a particular 4DI structural embodiment which uniquelyenables the integration of optical data communication capability between4DI modules is also described.

These and other aspects of the present invention are delineated infurther detail using the following illustrative drawings and thesubsequent descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings also set out the invention and areincorporated in and constitute a part of the disclosure along with thisspecification and are included to illustrate various embodiments of theinvention and together with this written description also serve toexplain the principles of the invention. These drawings, however, arenot necessarily drawn to scale.

In the drawings:

FIG. 1 comprises an isometric view of the inventive 4DI module showing aprocessor chip attached atop a vertical stack of device slices bondedtogether with an adhesive along with C4 input output pads at the bottom.

FIG. 2 comprises a perspective view showing the detail of a 90 degreecorner connection between the ends of metal wiring on the verticalslices and the metal pattern on the top surface of the assembledvertical slice stack of the present invention.

FIG. 3 comprises a chart of calculated data illustrating the effectivearea multiplier relative to a 2D memory achieved through the verticalmemory slice stacked 4DI configuration of the type shown in FIG. 1 ofthe present invention.

FIG. 4 comprises a chart of calculated data estimating the number ofunique interconnections possible per square millimeter using the slicesurface wiring and the 90 degree corner connection arrangement of the4DI assembly of the present invention.

FIG. 5 comprises a plan view showing the inventive template assemblycomprising a carrier wafer and several frame wafers of the presentinvention and a side elevation taken along the line A-A of the templateassembly

FIG. 6 comprises a flow chart illustrating the main steps in thefabrication of the carrier wafer, frame wafers and the steps to form thetemplate assembly resulting in the structure of FIG. 5 of the presentinvention.

FIG. 7 comprises a plan view showing the assembled grouping of verticalwafer slices on a template assembly to achieve a wafer like substrateformat enabling full wafer process tooling compatibility of the presentinvention.

FIG. 8 comprises a side elevation in cross section of a system of thepresent invention comprising multiple 4DI modules mounted on a packagingsubstrate, each 4DI module being provided with optoelectronic devicesfor sending and receiving optical signals and for electro-opticconversion located on the end faces of their vertical slice assembly toenable optical communication between the logic processor chips in theadjacent 4DI modules or by a optical fiber ribbon to 4DI modules locatedon a different packaging substrate.

DETAILED DESCRIPTION

FIG. 1 shows a schematic isometric view of a 4DI final assemblycomprising a logic microprocessor chip 100 attached to a collection ofvertically stacked slices 200 and 300 through microjoints 500. Slices200 and 300 are typically slices from memory wafers but in one laterembodiment the end slices 200 are chosen to be slices from anoptoelectronic device wafers. The view also shows the metal wiring lines400 running along the vertical face of one of the end slices 200 andthese lines are connected to circuitry present in the slice. Althoughthe lines are shown only on this end slice for clarity, such lines areprovided on the active surface of all of the slices 200 and 300. At thebottom of the slice stack an array of C4 solder joints 900 are shownwhich enable attaching the whole 4DI assembly to a packaging substrate(not shown). Microjoints 500 and C4 solder joints 900 connect tometallization patterns (omitted in FIG. 1 for clarity) located on thetop and bottom surfaces of the slice assembly respectively. Thesemetallization patterns in turn are connected to the ends of the slicesurface wiring lines 400 thus enabling electrical connections betweenthe logic microprocessor 100, circuitry in slices 200 and 300, and thepackaging substrate (not shown in FIG. 1 for clarity). Although only sixvertical slices are shown in FIG. 1 for simplicity of illustrating theconcept, as will be evident from the subsequent description, any numberof vertical slices can be present in the 4DI structure depending uponthe area of the microprocessor chip 100 and the thickness of theindividual vertical slices 200 and 300. It should be additionally notedthat the adhesive layer used to bond the vertical slices to each otheris not shown in FIG. 1, again for clarity but will be described in thedetails of the next figure.

Details of the corner connections between slice surface wiring lines andthe top metallization patterns are shown schematically in FIG. 2 whichis a cut out and close up view of a portion of the top surface of thevertical slice assembly. Two interior slices 300 and 300′ are shown forillustrative purposes and they are bonded to each other using anadhesive layer 600. Also shown are the top ends 410 of slice surfacewiring (400 from FIG. 1) on the surface of slice 300′ surrounded byadhesive 600. Top surface metal patterns 700 connect to slice surfacewiring line ends 410 making 90 degree corner connections. Similarconnections are also made to the other end of the slice surface wiringlines to bottom surface metal patterns not shown in FIG. 2. These topand bottom surface wiring patterns fan out to microjoints and C4 solderpads respectively in the final structure (shown in FIG. 1 but omitted inFIG. 2 for clarity).

Thus electrical interconnection is provided between the logicmicroprocessor chip 100 and the circuitry on the vertical slices 200 and300 by means of microjoints 500 (of FIG. 1), top surface wiring 700 (ofFIG. 2) and slice surface wiring 400. Delivery of power, ground andexternal input output signals to and from the logic microprocessor 100and vertical slice circuitry are enabled by additionally using thebottom surface wiring pattern (not shown) and the C4 solder connections900 to the package substrate (not shown).

Even though a single layer of slice surface wiring 400 is shown in FIG.1 for simplicity of illustration, multiple wiring and via levels will bepresent on the active surface of the slice, some of which may be used asground or power planes. To increase the area of the corner contactbetween top surface wiring 700 and the slice surface wiring, withoutincreasing the corner crossing pitch, in the region of the contact 410multiple wiring levels on the slices will be stacked and electricallyconnected together by vias. Also, the top surface wiring 700 is shown toextend slightly beyond the surfaces wires end 410 to allow for anelectrical contact to be made to the surface wiring line ends 410 evenif there is some variation in the slice 300 thickness which would causethe locations of the surface wiring line ends to vary slightly acrossthe assembly of slices. Additionally, although the top surface wiring700 is shown as a single wiring level, more complex interconnect schemessuch as multilevel wiring comprising repeating combinations of a wiringlevel and an insulator coating with via contact openings filled withmetal connecting to the wiring level, and terminating on top with acontact metal level suitable for connecting to microjoints 500 wouldalso be used in 4DI assemblies as required. Similarly on the bottom sideof the slice stack, a similar multilevel interconnect scheme terminatingwith a contact metal level suitable for connecting to C4 solder ballswould most likely be used in 4DI assemblies,

FIG. 3 is a summary of an exemplary calculation showing the memorydensity per unit foot print area of the logic microprocessor chippossible in the 4DI configuration expressed as a multiplier of a casewhere a single horizontally placed memory layer is bonded to the logicchip as in the case of a logic plus single memory bonded 3DI stack.Increased memory content and hence a higher multiplier is possibleeither by making the vertical slices thinner (0.735 mm is the typicalthickness of a standard unthinned wafer) or by making the memory slicestaller as shown in FIG. 3. To cite an example of how to use theinformation in FIG. 3, a 10× multiplier compared to a single 3D memorylayer (or alternately stated an equivalence to 10 memory chips stackedon a logic chip using state of the art 3DI methods) is possible using0.200 mm thick×2 mm high memory slices stacked vertically in the 4DIstructure. Since no loss of silicon area due to TSV connections betweenthe logic and the memory layer is assumed for the standard 3DI stack inthis comparison, the multiplier is a highly conservative estimate of theenhancement afforded by the 4DI structure compared to 3DI structureswith TSV's. Although, only a limited range of slice thickness and heightvalues are shown in FIG. 3 it is understood that if processing andhandling methods would allow, one could change these parameters tovalues beyond those shown in the table to achieve even highermultipliers than shown in FIG. 3 without deviating from the spirit ofthe present invention.

FIG. 4 illustrates the other important benefit of the 4DI configuration,namely the high communication bandwidth between the logic microprocessor100 and the circuitry in the vertical memory slices 200 and 300 orpackage substrate. As the communication channels are provided by slicesurface wires 400 which are fabricated using traditional thin film backend of the line (BEOL) processing on standard silicon wafers, they canpotentially be fabricated at a much finer pitch compared to TSV's whichare limited by processing and silicon thickness considerations asmentioned earlier. Further, using thinned vertical memory slices allowsmore memory slices with their associated slice surface wiring availableclose to the microprocessor circuitry in the logic chip 100. This isnumerically illustrated in FIG. 4 where the number of unique logic tomemory communication channels accessible per square mm of the logic chipfoot print are shown for different memory slice thickness values anddifferent line to line pitch for the slice surface wiring at the cornercrossing to the top surface metal. As an example, using the table for atypical logic chip with a 400 sq. mm. foot print, using memory sliceswhich are 0.200 mm thick, with a very relaxed ground rule slice surfacewiring at 10 um pitch, a total of up to 200,000 unique communicationlines would be possible between the logic processor and the associatedmemory bank located below the same. Some of these connections will needto be used for power, ground, and system input/output. One key benefitof the present inventive 4DI approach is that such memory density andmemory access capability is achieved without the need for TSV's and theassociated design and process complexities introduced. Memory cubeapproaches in the prior art some times invoke the vertical stacking ofmemory chips but they use memory access lines which are bused togetherand provided after the cube assembly and hence only allow a much lowerinterconnect density and hence do not enable the memory bandwidthpossible in 4DI.

FIG. 5 through 7 describe an inventive method that enables the assemblyof numerous vertical device wafer slices into a wafer-type format on acarrier to facilitate ease of processing the vertical stack to form topand bottom surface wiring patterns and the like. The method uses some ofthe elements disclosed in United States Patent Application DocketYOR92009-0121US1 for post processing after the carrier/frame assemblyand teaches additional unique features to facilitate full wafer-typeprocessing of the slice stacks.

FIG. 5 shows a plan view and a sectional view of a template assemblycomprising a carrier wafer 1000 and several frame wafers 2000. Framewafers 2000 have windows 2500 cut out and separated by webs 2600.Several frame wafers are attached on the carrier wafer and to each otherand windows 2500 are precisely located relative to the carrier waferusing back side alignment marks previously formed on the carrier wafer.The whole stack is bonded together using an adhesive layer disposed oneach wafer leading to a template assembly shaped like a thick wafer withpockets at the locations of the windows 2500.

One inventive process flow for fabricating the template assembly shownin FIG. 5 and its use to then incorporate vertical device wafer slicesis described schematically in the flow chart comprising FIG. 6. In thefollowing description the vertical device wafers will be referred to asthe memory wafers as these are the most common device wafers to be usedin the 4DI assembly. It should be noted that other types of devicewafers can be similarly processed into vertical stacks and incorporatedinto 4DI assemblies and the descriptions below would apply in a generalmanner to all these cases without deviating from the spirit of theinventive method described.

The process flow of FIG. 6 comprises multiple blocks containing specificprocess sequences performed on the frame wafers, carrier wafer and thememory wafers and making a template assembly and the wafer format sliceassembly.

Blocks 1 and 2 describe the process steps performed to create thecarrier wafer 1000. In the sequence contained in block 1, silicon wafersare processed to create suitable reference alignment marks on their backsurfaces. Such marks can be made of metal features, etched intodeposited or grown insulators such as silicon oxide or nitride, orsimply etched as a cavity into the silicon surface itself.

In process block 2, a photoimageable adhesive is applied on the topsurface of the carrier wafer 1000 and photopatterned using standardphotolithographic methods and by locating the pattern precisely on thetop surface using as reference the back side alignment marks previouslyformed on the wafer, Double sided lithography tools known in the artsuch as MA-8 manufactured by Suss Microtec Inc. can be used to form thenecessary photopatterns for using such back aligned marks. Thepatterning of the adhesive is done such that there is no adhesive in thelocations corresponding to where the windows of the frame wafers will belocated in the final assembly. The purpose for this particular patternwill be explained subsequently. The photoimaged adhesive is preferablybaked at some intermediate temperature such that it is tack free andsubstantially free of residual solvents and yet pliable and conducivefor bonding later. Typically 150 C for 15 minutes is an adequate bakingprocess but any suitable temperature that precludes the significantonset of cross linking and setting of the adhesive and yet removesresidual solvents is acceptable. Typical adhesives suitable for this useare photosensitive polyimides such as HD-4004 manufactured by HDMicrosystems Inc. These afford good bonding characteristics andstability to 400 C for post bonding process steps required for the 4DIprocess. Blocks 1 and 2 complete the processing required to form thecarrier wafer 1000

Block 3 describes the flow required to form a frame wafer. Many framewafers will be required to form a template assembly as shown in FIG. 5.In block 3 an adhesive is applied, and soft baked on the front side offrame wafers. Photopatterning is not required but can optionally be usedto create vent channels free of adhesive which can help the escape ofany outgased species during subsequent lamination step. Also it shouldbe noted that some frame wafers are not provided with any adhesivecoating and these will be used in assemblies as the top most frame waferas described later.

Process blocks A through D describe the steps required to assemble framewafers and a carrier wafer to produce a template assembly. In processblock A, the carrier wafer is placed face up and a frame wafer is placedfacing up on it in rough alignment using mechanical means such asalignment of the wafer notches. Additional frame wafers with adhesivecoating are stacked in the same fashion finishing the stack with a framewafer with no adhesive coating as the top most wafer in the stack. Thetotal thickness of the frame wafer stack is targeted to be equal to theheight of memory wafer slices to be produced in process block I as willbe described later. In process block B, the stack of carrier and framewafers is subjected to high temperature and pressure to laminate themtogether using the adhesive layers provided on their surfaces.Lamination temperature is chosen to be above the point where theadhesive is able to flow and fill any gaps between the wafers and tocross link and set into a permanent bonding layer. Typically atemperature between 300 and 400 C and a pressure of about 100 to 300 psiare suitable for this purpose. Isostatic lamination using gas bladdersto exert uniform pressure on the stack is preferred although parallelplate lamination presses could also be used.

In process block C, windows are created in the frame wafers in thelaminated structure. It should be recalled that the adhesive wasexpressly excluded on the front side of the carrier wafer at the areaswhere the windows in the frame wafers are expected to be present, andhence only the remaining areas are bonded together between the carrierwafer and the lowest wafer in the frame wafer stack. Next, dicing marksthat define the outline of the windows are formed on top of the top mostframe wafer referencing the patterns with respect to the back sidealignment marks provided on the carrier wafer. This enables the locationof the boundaries of these windows in precise registration to theadhesive free areas provided on the front side of the carrier wafer.

In process block D, cuts are made into the stack along the boundariesdefining the windows going all the way through all the frame wafers anda little depth into the carrier wafer. These cuts can be made with awafer dicing saw or a wire saw where the depth of the cut can becontrolled to micron type accuracy. When such cuts are made, theportions of the frame wafers corresponding to the window areas wherethere is no adhesive present on the carrier wafer get released and canbe removed (as the bottom most frame wafer is not adhered to the carrierin these areas) while the remaining area of the frame wafers includingthe webs 2600 stay adhered in the template assembly. In block E ofprocessing, a photosensitive adhesive is again applied but this timedispensed or patterned to be present only in the window/cavity areas2500 of the template assembly. Alternately, a non-photosensitiveadhesive could be selectively applied in the window/cavity areas 2500 bya method such as spraying through a contact metal mask or screeningthrough a stencil with appropriate window openings. The final structurehas this final adhesive present only on the carrier wafer top surfaceand only in the window/cavity areas 2500. The resulting structure wouldbe the template assembly shown in FIG. 5.

Next in process block I, memory slices are created starting with memorywafers and providing them with top surface fan out wiring connecting tothe various memory circuits contained within. As mentioned earlier,multiple interconnect levels with wiring and vias could be utilized toaccomplish this result. In block II, they are co

with photosensitive adhesive which is patterned to be excluded from thedicing channels along which the wafers will be diced into slicessubsequently. In block III these wafers are stacked together, laminatedand then diced into slice stacks. Alternately, one could first dice theadhesive coated memory wafers into long slices and then laminate theslices together to form the slice stack. In either case, the number ofslices in the final stack and hence the stack thickness is chosen suchthat the stack will snugly fit into the cavities 2500 in the templateassembly from Block E, when the slice stack is tipped such that the fanout metal patterned faces are oriented in the vertical direction.

In process block IV, the prebonded slice stacks (5000 shown in FIG. 7)are loaded into the cavities in the specific orientation describedearlier. The whole structure is then subjected to isostatic laminationsuch that slice stacks are well bonded to the carrier wafer by theadhesive present on the surface of the carrier wafer in the pocket areasand fully confined within the cavities 2500 resulting in the structureshown schematically in FIG. 7. This structure, comprising the carrierwafer 1000 (hidden underneath in the plan view of FIG. 7), frame wafers2000 with vertical slice stacks 5000 located within pockets in framewafers 2000 separated by webs 2600 is designated as the wafer formatslice assembly 6000 and resembles a thick silicon wafer. It is conduciveto wafer format processing to be performed on all the slice stack groups(5000) en masse using semiconductor wafer or packaging manufacturingtools currently known in the art. This substrate format enablesefficient processing of multiple slice stacks in one pass withoutconcerns regarding handling of fragile slices or cubes with non-standardsubstrate sizes. Thus the quality and feature size of patterns which canbe fabricated atop such a wafer format slice assembly is far superior tothose possible when individual slices or slice stacks or cubes areprocessed as in the prior art.

Subsequent processing steps described in application YOR9-2009-0121 cannow be performed on this wafer format slice assembly conveniently. Anexemplary sequence as described in the above application and added herefor the sake of completion would include: grinding and polishing of theslice stacks to expose the ends 410 of the fan out wiring 400 (see 400in FIGS. 1 and 410 in FIG. 2) on the faces of the memory slices;recessing the silicon around the wire ends; depositing and planarizing alayer of dielectric such as silicon oxide or nitride to provideelectrical isolation; and depositing and patterning top surface metalpattern (700 of FIG. 2) to make corner connections to slice surfacewiring ends (410 of FIG. 2). Metal contact pads for enabling microjointconnections to logic chip are also formed as part of the top surfacemetal pattern (700 of FIG. 2). These pads can be made to extend slightlybeyond the surface wiring ends 410 shown to allow for tolerances in theslice thickness and adhesive layer thickness as mentioned earlier.Additionally, more complex interconnect schemes such as multilevelwiring comprising repeating combinations of a wiring level and aninsulator coating with via contact openings filled with metal connectingto the wiring level, and terminating on top with a contact metal levelsuitable for connecting to microjoints 500 could also be used in such4DI assemblies as required.

At this point, a handle substrate is attached to the processed top sideof the wafer format slice assembly. The structure is flipped over andthe carrier wafer is ground or etched away fully and the back side ofthe slice assembly is ground and polished to expose the bottom ends ofslice surface wiring. Back side metal patterns to make cornerconnections with the bottom ends of slice surface wires, which caninclude a wiring level, insulator layer with metal filled via contactsconnecting to the wiring level and a suitable contact pad metallurgylocated on the insulator to support solder and finally C4 solder balls(900 in FIG. 1) are then formed on this surface. Typically theinterconnect wiring and via levels utilize conductive metals such ascopper, aluminum or alloys thereof. Contact pads to support solder in C4balls or solder microjoints typically comprise a stack made of metalsselected from copper, nickel, cobalt, titanium, palladium, platinum andgold with the noble metals being on top to provide wetability of solderand the other metals provided below the noble metal to enable solderreaction barrier function. The structure is then diced through the slicestack and the handle wafer into coupons that are the same size as thelogic processor chip. The structure is then mounted on to a packagingsubstrate by means of the array of C4 solder balls 900. The section ofthe handle wafer still attached on the top side can then be removed fromthis structure by grinding or laser release methods known in the art.The logic processor chip 100 with microjoint metal, 500 in FIG. 1, isthen attached to the exposed top surface metal patterns on the memoryslice stack coupon completing the 4DI structure shown in FIG. 1 whichwould in this case be mounted on a packaging substrate (not shown inFIG. 1).

Microjoint metal 500 in this flow would be a solder and a reflow joiningprocess is utilized to achieve this connection. Alternate joiningmethods for attaching the processor chip to the memory slice assemblysuch as transfer and joining (TJ) described in YOR9-2009-0121US1 canalso be used. These methods would require copper to copper or gold togold bonding supplemented by an adhesive layer for additional bondstrength. In this case, the processor chips may be attached in lieu ofthe handle wafer in the above flow using the TJ method first and can beleft in place for the remaining process steps mentioned above. Handlewafer attach, removal as well the solder microjoint formation will notbe required in this case.

The 4DI structure with vertical slice assembly shown in FIG. 1 can beused advantageously to enable other functional capability in themodules. One exemplary depiction of a specific embodiment is shown inFIG. 8. FIG. 8 shows an elevation view of two 4DI modules 3001 and 3002mounted on a package substrate 4000. 4DI modules 3001 and 3002 areparticular embodiments of the module shown in FIG. 1 and incorporateoptoelectronic devices in the two end slices of the vertical stack.These devices include but are not limited to light emitting laser VCSEL(vertical cavity surface emitting laser) elements, drive circuits tooperate the VCSELS, optical transmitter and receiver elements,electro-optic modulating circuits, electro-optic conversion circuits,optical focusing/collimating elements, devices for aligning or couplinginto optical fiber connectors, optical wave guides, photodetectors, andthe like. These slices are also provided with the corner connections tothe processor chip and the C4 balls as in the case of the memory onlyslices which comprise the interior slices in the stack. These end slicesare positioned in the stack with their active device surface facingoutwards. The end slice in each module is designed to communicate withthe processor chip above and receive electrical signals which areconverted by the devices in the end slice to optical signals as well asconvert any received optical signals back to electrical signals forsending back to the processor chip above.

These optical signals (photons of laser energy) are emitted outward fromthe slice surface and are then either coupled into an optical transferdevice 7000 or a ribbon fiber coupling device 7100. If the gap between4DI modules 3001 and 3002 is sufficiently small and the alignmentbetween the light emission devices on one 4DI module and the photondetecting devices on the facing 4DI module is good enough, an opticaltransfer device 7000 may not be required. If these conditions are notmet and an optical transfer device 7000 is required, then appropriateoptical elements can be used to expand and collimate the emitted light,and then focus it onto the photo detecting device. Alternatively, adevice which limits the divergence of the emitted light such as a fusedfiber bundle, or suitable wave guide, can 7000 serves to improve thecoupling of the emitted light to the photon detecting devices and toreduce the cross talk between adjacent 7100, such as an MT ferrule, isaligned & optically coupled to and optical end slice 202. Note that theribbon fiber coupling device 7100 can be mechanically attached to theend slice 202, as shown, or additionally to the substrate 4000, or toboth (not shown). An optical fiber ribbon 7300 which is terminated witha mating ribbon fiber coupling device 7200, such as an MT ferrule, isshown in FIG. 8, not connected to, but adjacent to ribbon fiber couplingdevice 7100.

It is advantageous to integrate the optical communications device asclose to the processor chip as possible to enable a high data rate, hightotal data bandwidth, and reduced power consumption. If the opticalcommunications device is mounted on the package substrate 4000, asignificant number of the C4 balls 900 may be required to carry theelectrical signals and the power consumed moving the data to and fromthe optical communications device would be increased.

In the configuration described above, an electrical signal fromprocessor chip 101 is sent to end slice 201 where it is converted to anoptical signal and emitted outwards to the right. The optical signalemanating from end slice 201 in module 3001 is directed to and receivedby the receiving end slice 202′ of the 4DI module 3002. Appropriatedevices in slice 202′ convert the optical signal to electrical signalsand communicate the same to the processor chip 102 mounted thereon. Thuscommunication between processor chips 101 and 102 are enabled usingcircuitry contained within 4DI modules 3001 and 3002 without using anyinput output C4 connections or electrical pathways in the packagesubstrate 4000. As optical data communication accommodates a large bandwidth and is free of signal distortions, delays and losses associatedwith long electrical communication means through a packaging substrate,this arrangement can enable very large bandwidth data transfer at a highfidelity between neighboring 4DI modules in a system ensemble and reducethe communication load required through the package substrate 4000.

Although the configuration and communication methodology is illustratedabove using just two modules, it is clear that it can be extended tomore such modules located in a linear arrangement on a common substrate.Such a methodology would be highly conducive to building computingsystems wherein 4DI modules are organized into well coordinated parallelcomputing engines optimized to solve unique problems requiring largedata transfer rates between modules. In similar fashion, using ribbonfiber coupling device 7100, 4DI modules located on different packagesubstrates 4000, different system boards, or in different racks (detailsnot shown in Figures) can be optically interconnected as well.

Throughout this specification, abstract of the disclosure, and in thedrawings, the inventors have set out equivalents, including withoutlimitation, equivalent elements, materials, compounds, compositions,conditions, processes, structures and the like, and even though set outindividually, also include combinations of these equivalents such as thetwo component, three component, or four component combinations, or moreas well as combinations of such equivalent elements, materials,compositions conditions, processes, structures and the like in anyratios or in any manner.

Additionally, the various numerical ranges describing the invention asset forth throughout the specification also includes any combination ofthe lower ends of the ranges with the higher ends of the ranges, and anysingle numerical value, or any single numerical value that will reducethe scope of the lower limits of the range or the scope of the higherlimits of the range, and also includes ranges falling within any ofthese ranges.

The terms “about,” “substantial,” or “substantially” in any claim or asapplied to any parameters herein, such as a numerical value, includingvalues used to describe numerical ranges, means slight variations in theparameter. In another embodiment, the terms “about,” “substantial,” or“substantially,” when employed to define numerical parameter include,e.g., a variation up to five per-cent, ten per-cent, or 15 per-cent, orsomewhat higher or lower than the upper limit of five per-cent, tenper-cent, or 15 per-cent. The term “up to” that defines numericalparameters means a lower limit comprising zero or a miniscule number,e.g., 0.001. The terms “about,” “substantial” and “substantially” alsomean that which is largely or for the most part or entirely specified.The inventors also employ the terms “substantial,” “substantially,” and“about” in the same way as a person with ordinary skill in the art wouldunderstand them or employ them. The phrase “at least” means one or acombination of the elements, materials, compounds, or conditions, andthe like specified herein, wherein “combination” is defined above. Theterms “written description,” “specification,” “claims,” “drawings,” and“abstract” as used herein refer to the written description,specification, claims, drawings, and abstract of the disclosure asoriginally filed, or the written description, specification, claims,drawings, and abstract of the disclosure as subsequently amended, as thecase may be.

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All scientific journal articles and other articles, including internetsites, as well as issued and pending patents that this writtendescription mentions including the references cited in such scientificjournal articles and other articles, including internet sites, and suchpatents, are incorporated herein by reference in their entirety and forthe purpose cited in this written description and for all otherdisclosures contained in such scientific journal articles and otherarticles, including internet sites as well as patents and the aforesaidreferences cited therein, as all or any one may bear on or apply inwhole or in part, not only to the foregoing written description, butalso the following claims, abstract of the disclosure, and appendeddrawings.

Applicants reserve the right to amend this specification and thedrawings filed herein without prejudice or disclaimer and in doing so,they do not disclaim, abandon, or forfeit any invention directly orindirectly represented thereby, and hereby rescind any implieddisclaimer that may be inferred from applicants' amendments orcancellation in the course of prosecution of this or any parent,continuation, continuing, continuation in part, divisional, terminallydisclaimed, or foreign patent application (related patent application orapplications), and specifically preserve all and any inventions embodiednot only by the original claims but also the written description,abstract of the disclosure, and drawings of this application and anyrelated patent application or applications, and preserve the right toprosecute claims to these inventions in any related patent applicationor applications filed prior to or subsequent to the filing of thisapplication.

Although the inventors have described their invention by reference tosome embodiments, other embodiments defined by the doctrine ofequivalents are intended to be included as falling within the broadscope and spirit of the foregoing written description, and the followingclaims, abstract of the disclosure, and appended drawings.

We claim:
 1. A 4DI structure comprising a first substrate placed in ahorizontal orientation and attached to an assembly comprising a set ofsecond substrates bonded to each other and placed in a verticalorientation beneath said first substrate where there is an area array ofelectrical contacts between the two and said area array of electricalcontacts is formed by means of corner connections to wiring on the faceof said set of second substrates.
 2. The structure of claim 1 whereinsaid first substrate is a logic microprocessor chip and said set ofsecond substrates comprises slices of memory wafers.
 3. The structure ofclaim 1 wherein said first substrate is a logic microprocessor and saidsecond set of substrates further comprises a first subset of slicesplaced on the end faces of the vertical stack and made fromoptoelectronic device wafers and a second subset of slices placed in theinterior locations of the vertical stack and made from memory wafers 4.The structure of claim 1 where two or more surface wiring levels areprovided on said set of second substrates, said wiring levels areelectrically connected together at said corner connections.
 5. Thestructure of claim 1 where said corner connections extend laterallybeyond said surface wiring levels so as to enable tolerance variationsin thickness of said vertical slices.
 6. The structure of claim 3wherein said first subset of slices are placed with their active deviceface facing outwards.
 7. The structure of claim 3 wherein said firstsubset of slices are provided with optoelectronic devices selected fromthe group comprising vertical cavity surface emitting lasers, drivercircuitry for powering lasers, optical-electrical converter circuits,electro-optic modulator circuits, photodetectors, and opticalwaveguides.
 8. The structure of claim 7 where a ribbon fiber couplingdevice is operatively aligned to an optoelectronic device.
 9. Thestructure of claim 1 further comprising an area array of cornerconnections to the other ends of said multiple wiring levels on said setof second substrates and comprising additionally an area array ofcontact pad structures to support C4 solder balls.
 10. The structure ofclaim 9 wherein said contact pad structure further comprises a cornerconnection pad, an insulator with a via opening filled with conductivemetal and a contact pad thereon with a solder wettable metal stack. 11.The structure of claim 10 wherein said conductive metal is selected fromCu, Al and alloys thereof and said wettable metal stack is formed usingmetal selected from the group comprising copper, nickel, titanium,cobalt, palladium, platinum and gold.
 12. A structure comprising apackaging substrate upon which a multitude of 4DI substrates of claim 3are mounted so as to enable optical data communication between adjacent4DI substrates.
 13. A structure according to claim 12 further comprisingoptical communication means such as collimators, beam couplers, fiberbundles and the like situated on said packaging substrate to enableefficient coupling between said multitude of 4DI substrates on saidpackaging substrate or additional 4DI substrates located on adjacentpackaging substrates.
 14. A method of simultaneously processing amultitude of vertically stacked substrates comprising the steps offabricating a template assembly to house said multitude of verticallystacked slices and populating said template assembly with saidvertically stacked slices located inside rectangular pockets therein sothat they can be processed in a wafer like substrate format.
 15. Themethod of claim 14 wherein the fabrication of said template assemblyfurther comprises the steps of: fabricating a carrier wafer with a setof back side alignment marks and a photoimaged adhesive in selectedareas on the front side referenced to said back side alignment marks soas to form a first window pattern with windows free of adhesiveprecisely located relative to said back side alignment marks;fabricating several frame wafers with an adhesive and one top framewafer without said adhesive; stacking said carrier wafer and saidseveral frame wafers, with said top frame wafer placed on the top ofsaid stack and keeping them in rough registration to each other andlaminating the stack together by exerting temperature and pressure;patterning top side alignment marks and dicing reference marks on saidtop frame wafer registering to said back side alignment marks on saidcarrier wafer such that said dicing channels formed by cutting alongsaid dicing alignment marks define a second window pattern preciselyaligned to said first window pattern in said photoimaged adhesive onsaid carrier wafer; cutting and removing portions of said top andseveral frame wafers in the laminated stack at said second windowpattern locations which are free of adhesive on said carrier wafer,thereby creating a template assembly shaped like a standard wafersubstrate and provided with rectangular pockets bounded in said windowpattern and precisely located in reference to said back side alignmentmarks on said carrier wafer; and selectively applying an adhesive layerto be only present in the open areas of said carrier wafer exposedthrough said rectangular pockets in said template assembly.
 16. A methodaccording claim 14 wherein the preparation of said vertical slice stackscomprises the steps of stacking wafers provided with an adhesivecoating, bonding said wafers together and then cutting them and formingvertical slice stacks by turning them such that their cut edges arehorizontal and their adhesive coated faces are vertical.
 17. A methodaccording to claim 14 wherein said method of selectively applying anadhesive layer is accomplished by a process selected fromphotopatterning of a photosensitive adhesive using said set of topsurface alignment marks on aid top frame wafer as reference or applyingan adhesive through a contact metal mask or stencil.
 18. A methodaccording to claim 16 wherein said vertical slice stacks are fabricatedsuch that the length and width of the said vertical slice stacks areprecisely selected to fit snugly into said rectangular pockets in saidtemplate assembly of claim
 14. 19. A method according to claim 14wherein said populating of said vertical slice stacks into said templateassembly is accomplished by loading said vertical slice stacks into saidrectangular pockets and applying temperature and pressure to bond saidvertical slice stacks to said carrier wafer using said patternedadhesive thereon.
 20. A method according to claim 16 wherein the slicescomprising said vertical slice stack are made from a memory wafer.
 21. Amethod according to claim 16 wherein at least two of the slices whichare located at the ends of said vertical slice stacks compriseoptoelectronic devices and said slices are positioned with their activedevice face facing out from said vertical stack.
 22. A method accordingto claim 21 wherein said optoelectronic device are selected from thegroup comprising light emitting laser VCSEL (vertical cavity surfaceemitting laser) elements, drive circuits to operate the VCSELS,transmitter and receiver elements, electro-optic modulating circuits,electro-optic conversion circuits, photo detectors, optical wave guidesand the like.
 23. A computing system comprising at least two of 4DImodules arranged adjacent to each other on a packaging substrate, saidat least two of 4DI modules further comprising a logic microprocessorchip attached to a group of vertical device wafer slices, said groupfurther comprising end slices made from optoelectronic device wafers andinterior slices made from memory wafer slices such that data exchangebetween said at least two 4DI modules is performed using opticalcommunication means employing said optoelectronic devices in said endslices.
 24. A system according to claim 23 further comprising opticalcoupling means such as collimators, fiber bundles to improve the opticalcoupling between said adjacent 4DI modules on said packaging substrateas well as enable optical coupling between 4DI modules on a plurality ofsaid packaging substrates.